1. Field of the Invention
The present invention is generally related to climbing aids. More particularly, this invention is related to mechanically expanding climbing aids which engage cracks in rock and function as a secure anchor to protect climbers by either preventing or arresting a fall.
2. Description of the Prior Art
Climbers utilize rope, slings, harnesses and a variety of mechanical devices as climbing aids to assist and protect their movement over rock. The climbing aids serve as a means to securely anchor the rope, and thereby the climber, to the rock face for the purpose of either preventing or arresting a fall.
During a climb and especially in the event of a fall, the climber's safety is dependent on the security of numerous anchors. Consequently, it is imperative that an anchor be able to withstand not only the weight of the climber but also the inertial forces generated when the rope arrests a fall.
A secure anchor can sometimes be accomplished by wedging a solid object of fixed shape into a crack in the rock. Such solid, fixed shape climbing aids are known in the climbing community as chocks or nuts. Chocks and nuts are available in a variety of shapes and sizes in order to accommodate variations in the shape and width of the cracks which a climber may encounter.
U.S. Patents have issued which describe solid, fixed shape chocks and nuts. For example, U.S. Pat. No. 3,948,485 entitled "Irregular Polygonal Mountaineering Chock" issued to Yvon Chouinard and Thomas Frost on Apr. 6, 1976 teaches a polygonal shaped chock. U.S. Pat. No. 4,082,241 entitled "Chock for Mountain Climbing" issued to John Brent on Apr. 4, 1975 teaches a chock for mountain climbing which is in the form of a truncated pyramid. U.S. Pat. No. 4,422,607 entitled "Climbing Chocks" issued to Mark Vallance on Dec. 27, 1983 teaches a chock having a generally wedged shaped body with two opposite side faces of which are respectively of concave and convex configuration.
Climbing aids of solid, fixed shape are not very effective in wide, smooth, parallel sided, or openly flaring cracks. For such applications, mechanically expanding climbing aide have been developed. For example, U.S. Pat. No. 3,877,679 entitled "Anchor Device for Mountain Climbers" issued to Greg Lowe on Apr. 15, 1975 teaches a climbing aid which includes a body having an arcuate cam surface which is configured to spiral outward to the rock as it rotates about a pivot. U.S. Pat. No. 4,184,657 entitled "Climbing Aids" issued to Raymond Jardine on Jan. 22, 1980 teaches a climbing aid which includes two pairs of cam members which are pivotally mounted on a single spindle and are shaped such that movement progressively spirals the cam surfaces outward thereby jamming the climbing aid within the crack. U.S. Pat. No. 4,565,342 entitled "Anchoring Device for Rock Climbing" issued to Robert Grow on Jan. 21, 1986 and U.S. Pat. No. 4,575,032 entitled "Rock Climbing Adjustable Chock" issued to Peter Taylor on Mar. 11, 1986 both teach single axle, multi-cam devices similar to the climbing aid of Jardine.
All of the mechanically expanding climbing aids described supra have shortcomings which limit their usefulness. High jamming forces, which are generated when a load is applied, are directed to and concentrated at the ends of a single, relatively long shaft which can lead to structural failure due to bending. Spaced, staggered mounting of opposing cam members on the common shaft produce high bending couples, which can also lead to structural failure. Pivoting cam member on a common shaft necessitates a relatively tight cam surface curvature which concentrates frictional forces over a small contact area, resulting in rapid cam wear. Some loading situations force the climbing aid sideways which act to bend and break the rigid components, thereby leading to potentially catastrophic failure. Also, although the climbing aid expanding members typically swing through a 90.degree. arc from fully retracted to the fully expanded position, only the central 45.degree. arc of movement is practical for use, thereby requiring that a relatively large number of mechanically expanding climbing aid sizes be carried in order to accommodate the full range of crack widths which a climber may encounter.
In view of the shortcomings characteristic of the prior art, an improved mechanically expanding climbing aid was taught by the applicant's Application Number 780,375 filed Sep. 26, 1985 now U.S. Pat. No. 4,643,377 which issued Feb. 17, 1987. The applicant's improved mechanically expanding climbing aid features two parallel axles on which opposing cam members rotate separately with crossed radii. As a result of the double axle structure, the cam members closely intermingle when retracted thereby significantly increasing the useful range of cam member movement from fully retracted to fully expanded. Consequently, a lower number of sizes are needed by the climber to accommodate the range of crack widths encountered while climbing. Because the cam member rotational radii are crossed and subsequently longer than radii of an equivalently sized single axle climbing aid, leverage and the resulting anchoring force are significantly greater. Similarly, because the cam member arcuate outer surface curvature is broader than that of an equivalently sized single axle climbing aid, the contact area with the crack walls is increased thereby reducing cam surface wear. Also, because bearing loads are shared equally by two axles instead of a single axle, the improved mechanically expanding climbing aid avoids structural failure due to high bending forces and couples.
The climbing aid taught by U.S. Pat. No. 4,643,377 is marketed under the trade name "Camalot". Camalot is manufactured in a range of overlapping sizes to accommodate crack widths from 2 to 18 cm (3/4 to 7 inches). The various overlapping sizes are essentially the same configuration with the component dimensions scaled up or down to achieve the desired expansion range. Scaling the Camalot double axle configuration small enough to accommodate crack widths under 2 cm has not been practical due to physical constraints. For example, 4 mm is the smallest useful diameter for an axle of adequate strength using state of the art materials, and it is not possible to have parallel 4 mm diameter axles spaced to mount interlocking cams and also have an assembly thin enough to provide the clearance needed to slip into cracks less than 2 cm wide. Even so, there is significant need in the climbing community for mechanically expanding climbing aids which can be placed in cracks under 1 cm wide and also have the wide expansion range and strength provided by cam members pivoting with crossed radii.